unreliable detection of PB1 eeprom on V4

Sometimes the EEprom of the first peripheral board does not get detected on boot. sometimes it does.

I can swap board 1 with board 8, and the issue seems to be linked with slot 1, not board specific._

I don't know if the I2C bus is left somewhat in a bad state, or if the timing of the mux needs to be checked, or whathever, but since board detection depends on the eeprom file presence, this is somewhat critical...